chore: typo fixes and added import for examples (#19)

this may help fresh user to copy/paste and run smoothly

Author: wey-gu

README-CN.md

@@ -59,8 +59,13 @@ nebula-algorithm 是一款基于 [GraphX](https://spark.apache.org/graphx/) 的
    ```
    * 定义算法参数调用算法（以`PageRank`为例）
    ```
+   import com.vesoft.nebula.algorithm.config.{Configs, PRConfig, SparkConfig}
+   import org.apache.spark.sql.{DataFrame, SparkSession}
+
+   val spark = SparkSession.builder().master("local").getOrCreate()
+   val data  = spark.read.option("header", true).csv("src/test/resources/edge.csv")
    val prConfig = new PRConfig(5, 1.0)
-   val louvainResult = PageRankAlgo.apply(spark, data, prConfig, false)
+   val prResult = PageRankAlgo.apply(spark, data, prConfig, false)
    ```
  
     其他算法的调用方法见[测试示例](https://github.com/vesoft-inc/nebula-algorithm/tree/master/nebula-algorithm/src/test/scala/com/vesoft/nebula/algorithm/lib) 。

README.md

@@ -69,8 +69,13 @@ Limitation: Due to Nebula Algorithm will not encode string id, thus during the a
    ```
    * Instantiate algorithm's config, below is an example for `PageRank`.
    ```
+   import com.vesoft.nebula.algorithm.config.{Configs, PRConfig, SparkConfig}
+   import org.apache.spark.sql.{DataFrame, SparkSession}
+
+   val spark = SparkSession.builder().master("local").getOrCreate()
+   val data  = spark.read.option("header", true).csv("src/test/resources/edge.csv")
    val prConfig = new PRConfig(5, 1.0)
-   val louvainResult = PageRankAlgo.apply(spark, data, prConfig, false)
+   val prResult = PageRankAlgo.apply(spark, data, prConfig, false)
    ```
    
     For other algorithms, please refer to [test cases](https://github.com/vesoft-inc/nebula-algorithm/tree/master/nebula-algorithm/src/test/scala/com/vesoft/nebula/algorithm/lib).

nebula-algorithm/src/test/scala/com/vesoft/nebula/algorithm/lib/PageRankAlgoSuite.scala

@@ -12,10 +12,10 @@ import org.junit.Test
 class PageRankAlgoSuite {
   @Test
   def pageRankSuite(): Unit = {
-    val spark         = SparkSession.builder().master("local").getOrCreate()
-    val data          = spark.read.option("header", true).csv("src/test/resources/edge.csv")
-    val prConfig      = new PRConfig(5, 1.0)
-    val louvainResult = PageRankAlgo.apply(spark, data, prConfig, false)
-    assert(louvainResult.count() == 4)
+    val spark    = SparkSession.builder().master("local").getOrCreate()
+    val data     = spark.read.option("header", true).csv("src/test/resources/edge.csv")
+    val prConfig = new PRConfig(5, 1.0)
+    val prResult = PageRankAlgo.apply(spark, data, prConfig, false)
+    assert(prResult.count() == 4)
   }
 }